Control for a signaling system



June 6, 1939.

J. L. DELVAUX 2,161,286 CONTROL FOR A SIGNALING SYSTEM Filed Oct. 27,1937 Inventor:

His A QtOPne Q Patented June 6, 1939 2,161,286 CONTROLFOR A SIGNALINGSYSTEM Jean L. Delvaux,.Paris, France,.assignor to General ElectricCompany, a corporation of New York Application October 27, 1937, SerialNo. 171,294 I In France January 21', 193i m' 'radio receiver anautomatic volume control of the delayed type which secures itsdelayedcharacteristic from the operation of an electron discharge device; s

A further object of my invention is to accom- 1'5- plish a delayed?operation of an automatic volume control by utilizing an electrondischarge device normally present and performing a particular functionin a signaling system separate and distinct from that of automaticvolume control. A still further object of my invention is to utilize anelectron discharge device having a plurality of elements connected-- toperform a particular function in a signaling. system, and to-securefromtwo of the elements the additional function of providing a delayoperation in an automatic-vol'umecontrcl arrangement.

Another object of my-invention is to provide a delayed automatic volumecontrol arrangement which uses a minimum number of electron dischargedevices and'has theadditional advantages of simplicity of constructionand reliability of operation. v v Thenovel features which rbelieve to becharacteristic of my invention are set forth with par- L, ticuiarity inthe appended claims. My invention itself, however, both astoitsorganization and method. of operation; together with furtherobjects and advantages thereof may best beunderstood by reference to thefollowing description taken'inconnection with the accompanying drawingin which Fig; 1 represents an embodiment of my invention and Fig. 2represents a modificatiorr thereof;

Referring to Fig. r of thedrawing, I' have illusw trated my invention.as embodied in a radio receiver' having an antenna. I; connected toground through the primary 2 of a radio irequencytransformer- 3 thetransformer having a secondary winding 4 tuned to adesiredlsignalfrequency by 50 a variablecond'enser 5. connected in series with" afixed condenser 6. Signal oscillations appearing across this tunedcircuitare impressed upon the grid I and the cathode'l of an: electrondis-- charge signal: amplifier The signal oscillaw tions: are amplifiedthe signal amplifier 9t and pass to additional signal amplifiers.represented conventionally as l which may comprise any desired number ofstages of amplification and may possibly include a converter arrangementfor converting and thereafter amplifying the signal oscillation at afrequency different from that of the original signal frequency. Thesignal oscillations thereafter pass through a transformer ll having aprimary winding l2 and a secondary winding l3' tuned by the respectivecondensers I4 10' and l5-to the frequency of the signal oscillation,which may be either the initial'frequency or the converted frequencywhere a. converter arrangement is used, and are rectified by the diodeelements: l1 and i8. of a'multi-element electron dis- 16 charge devicel9 Theaudio-- frequency component of the rectified signal oscillationappears as a. pulsating unidirectional electromotive force across apotentiometer 20. A portion of this electromotive force is transferredthrough a con- 20 denser 2|. and a resistor 22 to a grid 23 of thedischarge device I!) where it is amplified and passes to. an audiofrequency amplifier conventionally represented as 24 which may compriseany desirednumber of stages of amplification. 25 The electromotive forceasthus amplified passes through an output transformer 25 forreproduction by a reproducer 26'.

The electromotive force appearing across the potentiometer 20 is alsoconnected through a 3 filter comprising a resistor 21 and a condenser 29to a conventional automatic volume control circuit 28 connected to biasthe grid 1 of the signal amplifier 9 and the corresponding grid of suchother stages of the amplifier Ill as may be desired. The grid 1 of thesignal amplifier 9 is given a small negative bias which may, forexample, be obtained by the use of a resistor 30 and a parallelconnected condenser 3| connected between the cathode 8 and ground. Thecorresponding grid of 4 each amplifier stage Hito which the automaticvolume control potential is connected is biased with a negativepotential in a similar manner to that of the grid 1. The operation ofthe automatic volume control arrangement thus far described isconventional and will not be further amplified since it is wellunderstood in the art.

An indicator arrangement, for indicating that the receiver is tuned tothe frequency of a received signal oscillation, is provided by anelectron discharge device 3-2; commonly known as an electron-ray tubebut more popularly known as a Magic eye" tube. The'construction of thistube is shown and its operation explained in the United- States Patentto Wagner No. 2,051,189.

acts as a ray-control electrode and causesv a shadow to appear on thefluorescent surface of the anode 31 having a width proportional to thepotential of the anode 38 which inturn is dependent upon the potentialof the control circuit 28. The discharge device 32 thus constitutes anarrangement for indicating by the relative width of a shadow on thefluorescent anode 31 that the receiver is tuned to the frequency of areceived signal oscillation.

Inaccordance with my invention, I provide a delayed operation of theautomatic volume control by utilizing the grid 33 and the cathode 39 ofthe electron discharge device 32 in an arrangement which, in the absenceof a signal oscillation, maintains the diode anode IT at a smallnegative potential with respect to the diode cathode I8. To this end, aresistor 4| and a parallel connected condenser 42 are connected betweenthe cathode |8 of the discharge device 19 and ground. Space current inthe discharge device |9 flowing from the anode 43 to the cathode ispasses through the resistor 4! and causes the cathode l8 to have apositive potential with respect to ground. This positive potential isimpressed through the resistors 29 and 21 upon the grid 33 of theelectron discharge device 32 and, assuming the absence of a signaloscillation, the grid is thereby made positive with respect to thecathode 39 which is at ground potential. A current thereupon flowsbetween the grid 33 and the cathode 39 to produce a potential drop inthe resistor 29 of a polarity such that the diode anode I1 is maintainedslightly negative relative to the diode cathode l8. It may be noted atthis point that as long as current flows from the grid 33 to the cathode39, the automatic volume control circuit 29 remains at approximatelyground potential and the bias on the grid 1 of the signal amplifier 9has a value equal to the potential drop across the resistor 39.

This negative condition of the diode anode I1 is maintained until asignal having a predetermined amplitude of oscillation drives the anodell positive with respect to the diode cathode l8 at which time the diodeelements I! and I9 begin to rectify the signal oscillations to cause apotential drop across the resistor 29 of a polarity tending to make thegrid 33 of the discharge device 32 less positive. Current continues toflow between the grid 33 and the cathode 39 of the discharge device 32,however, until the amplitude of the signal oscillation appearing acrossthe condenser I5 is sufficient to drive the grid 33 negative withrespect to the cathode 39. When this occurs, a potential drop no longerexists across the resistors 29 and 27 caused by current flow between thegrid 33 and the cathode 39 of the discharge device 32 and any increasein the electromotive force appearing across the resistor 29 is noweffective as a control potential in the automatic volume control circuit28 which ceased to be at ground potential when current ceased to fiowbetween the grid 33 and the cathode 39 of the discharge device 32.

If the amplitude of the signal oscillation again decreases to a pointwhere the grid 33 of the device 32 becomes slightly positive, currentagain fiows from the grid 33 to the cathode 39 to cause a potential dropin the resistor 29 tending to drive the diode anode I1 negativeiw ithrespect to the diode cathode I8. And as before, current continues toflow from the grid 33 to the cathode 39, and the automatic volumecontrol circuit 28 continues to be at approximately ground potential,until such time as the amplitude of the signal oscillation increases tothe predetermined value necessary to drive the grid 33 negative.Thereafter the automatic volume control circuit 28 is efiective to. varythe gain of the signal amplifier 9.

I have shown in Fig. 2 a modification of my invention whereby thebiasing resistor 4| and condenser 42, whichare connectedin the cathodeto ground circuit of the discharge device I9, andthe biasing resistor 39and condenser 31, connected in the cathode to ground circuit of thesignal amplifier 9, may be eliminated and the cathodes 8 and !9connected directly to ground. In this figure, elements corresponding tolike elements of Fig. 1 are given likereference characters. Abattery 44is. connected.- between the cathode 39 of the electron discharge device32 and ground. In the absence of a signal oscillation, the battery 44maintains the control circuit 28 and thereby the grid 1 of the signalamplifier 9 at a small negative potential with respect to ground andproduces a current flow in. a circuit comprising. the resistors 29 and 21, the grid 33, and the cathode 39 of the discharge device 32 sufiicientto impress a small negative potential on the diode anode H with respectto the diode cathode 18 of the discharge device l9. A signal having therequired amplitude of oscillation produces a potential drop across theresistor 29 sufficient to drive the grid 33 of the discharge device 32negative with respect to the cathode 39 after which any additionalpotential drop across the resistor 29. is effective in the automaticvolume control circuit 28 to vary the gain of the signal amplifier 9.

While I have illustrated my invention by the use of an electron-ray typeof electron discharge device, it will be obvious that any similarelectron discharge device may be used which performs a similar function,or even a function totally unrelated to tuning indication, as long astwo elements of the discharge device operate in the absence of a signaloscillation with a substantially zero potential difference relative oneto another. It will further be obvious that the automatic control may bethat for an audio frequency amplifier as well as for the radio frequencyamplifier with which my invention is here shown and described.

While I have shown a specific embodiment of my invention, it will, ofcourse, be understood that I do not wish to be limited thereto sincemany modifications may be made in the arrangement of the system and inthe instrumentalities employed, and I therefore contemplate bytheappended claims to cover any such modifications as fall within the truespirit and scope of m invention.

What I claim as new and desire to secure by. Letters Patent of theUnited States is:

1. The combination, in a tunable radio receiver, of an electrondischarge signal amplifier having.

a variable gain characteristic, control means responsive to receivedsignal oscillations for varying the gain of said signal amplifier insubstantially inverse proportion to the strength of said signaloscillations, means responsive to said control means andincluding anelectron discharge device having a control grid and a cathode forindicating that said receiver is tuned to resonance with the frequencyof said signal oscillations, and means including the grid to cathodepath of said discharge device for delaying the application of control tosaid signal amplifier by said control means until said signaloscillations have a predetermined minimum strength.

2. The combination, in a radio receiver, of a variable gain electrondischarge signal amplifier, control means for varying the gain of saidampli fier in substantially inverse proportion to the strength ofreceived signal oscillations, an electron discharge amplifier havingelements including a grid, an anode and a cathode, means for supplyingto the input circuit of said last named amplifier a potential to beamplified, means associated with the output circuit of said last namedamplifier for utilizing amplified potentials, and means including thegrid to cathode path of said last named amplifier for terminating theoperation of said control means whenever said signal oscillations reacha predetermined strength.

3. The combination, in a signaling system, of an electron dischargesignal amplifier having a variable gain characteristic, means to varythe gain of said amplifier in substantially inverse proportion to theaverage amplitude of signal oscillations, an electron discharge directcurrent amplifier having elements including a control grid, an anode anda cathode, means for supplying to the input circuit of said last namedamplifier a unidirectional potential to be amplified, means associatedwith the output circuit of said last named amplifier for utilizingamplifier unidirectional potentials, and means including the controlgrid and cathode of said last-named amplifier for terminating thecontrol of said first named means whenever the amplitude of said signaloscillations falls below a predetermined value.

'4. In a signaling system, an electron discharge modulated-carriersignal amplifier, control means for varying the amplification of saidamplifier in substantially inverse proportion to the average carrieramplitude of signal oscillations, an electron discharge device having ananode, a grid, and a cathode, translating means connected to said anodeand to said cathode and operatively responsive only to negative valuesof biasing potential on said grid, and means connected to said grid andto said cathode and responsive only to positive values of biasingpotential on said grid for terminating the operation of said controlmeans whenever the amplitude of said signal oscillations acquires apredetermined value.

5. In combination, an electron discharge signal amplifier having acontrol grid, means responsive to the amplitude of signal oscillationsfor biasing said control grid, an electron discharge device having acontrol grid connected to be influenced by said means and having ananode and a cathode, translating means connected to said anode and tosaid cathode, and means for terminating the response of said first namedmeans whenever said signal oscillations fall be low a predeterminedamplitude, said last named means including means to impress a positivepotential on the control grid of said last named discharge device in theabsence of a signal oscillation.

6. The combination, in a signaling system, of a radio frequencyamplifier having a variable gain characteristic, means including animpedance for developing a control potential from signal oscillations,means utilizing said control potential for varying the gain of saidamplifier, an electron discharge amplifier having an anode, a cathode,and a control grid, means utilizing said control potential for biasingsaid control grid, and means including said impedance for giving saidcontrol grid a positive bias in the absence of signal oscillationswhereby the development of said control potential by said first namedmeans is delayed until said signal oscillations have a predeterminedamplitude.

'7. A delayed automatic volume control for a signaling apparatuscomprising, in combination, a source of signal oscillations, a variablegain electrode discharge signal amplifier connected to said source andhaving an output circuit, means associated with said output circuit andincluding an impedance for developing a control potential from signaloscillations appearing therein, means utilizing said control potentialto vary the gain of said signal amplifier, an electron discharge devicehaving elements including a grid and a cathode, said grid and saidcathode being connected to said output circuit, and a source ofpotential connected in a circuit including in series said grid, saidcathode and said impedance for maintaining the gain of said signalamplifier constant whenever the amplitude of said signal oscillationsfall below a predetermined value.

8. An electron discharge signal amplifier having a variable gaincharacteristic, automatic volume control means including an impedancefor regulating the gain of said amplifier, means responsive to signaloscillations for developing across said impedance a control potential,indicating means including an electron discharge device having a gridand a cathode for indicating the presence of signal oscillations, andmeans including a source of substantially constant electromotive forceconnected in a circuit comprising said impedance, said grid and saidcathode for developing across said impedance a control potential ofopposite polarity to that of said first named control potential wherebysaid second named means remains unresponsive to signal oscillationshaving an amplitude lower than a predetermined value.

JEAN L. DELVAUX.

